Note that user agents may choose to perform some of the steps involved in loading the
document speculatively prior to user navigation e.g. the user agent could pre-resolve the
host name, speculatively connect to the server hosting the document or prefetch the root
document ahead of the actual user navigation. The timings in the
PerformanceTiming interface represent the time
spent waiting after user navigation in these steps. For example, in the case of speculative
resolution that started and finished before user navigation and the user agent was able
to use that result, the domainLookupStart
and domainLookupEnd attributes should
both return the same value as
fetchStart. If the speculative resolution started
before user navigation and finished after navigationStart and the user agent
was able to use that result, the
domainLookupStart attribute should
return the same value as
fetchStart and the
domainLookupEnd attribute should return
the time immediately after the name lookup is successfully done.